Continuous bleaching method with an alkali metal chlorite containing an activator salt



CONTINUOUS BLEACHING METHOD WITH AN ALKALI METAL CHLORITE CONTAINING AN ACTIVATOR SALT Ernst Ruedi, Ennenda, Glarus, Switzerland, assignor, by mesne assignments, to FMC Corporation, New York. N.Y., a corporation of Delaware No Drawing. Filed Sept. 9, 1957, Ser. No. 682,640

Claims priority, application Switzerland Sept. 19, 1956 2 Claims. (Cl. 8-108) This invention relates to textile processing, and more particularly to continuous methods of bleaching textile material.

It is an object of the present invention to provide a continuous method of chlorite bleaching textiles by activation of an inactive chlorite solution, in a simple and inexpensive manner and with results vastly improved over methods previously proposed.

Other objects, and the manner in which they are attained, will become apparent as this specification proceeds.

The use of alkali chlorites, and particularly sodium chlorite, in the bleaching of textile material, and especially cellulose fibers, is a known expedient. Quite a number of methods have been proposed which aimed at solving the economic as well as technological problems arising in industrial practice, and particularly in the case of continuous processes, and a brief discussion of some typical ones of these prior art methods is considered advisable in order to properly distinguish the present invention.

The facts that in neutral or alkaline solutions, alkali chlorites are stable and their bleaching action is arrested, i.e. no chlorine dioxide is developed nor any other reaction takes place, as a decomposition of alkali chlorites occurs only in the presence of acids or other substances, suggested a bleaching method wherein the activation of the initially neutral or alkaline bleaching solution is effected only after it has been applied to the material to be bleached, by acidification. The advantages of this procedure, particularly with respect to a continuous process, are self-evident. This process has been disclosed in British Patent 723,566 and French Patent 1,100,066.

According to British Patent 723,566, the material to be bleached is impregnated with a non-acidic alkali chlorite solution and following the squeeze-off, for the purpose of activating the bleach effect, is exposed for 1 to 2 minutes to the influence of acid vapors, for example by treatment with a formic acid-steam mixture. This process failed to be adopted for a variety of reasons, and primarily because of violent corrosion in the steaming installation.

French Patent 1,100,066 discloses a continuous process using for the impregnation, a non-acidic alkali or alkaline earth chlorite solution containing an addition of esters of organic acids. By heating the moist, impregnated material to be bleached to about 100 C., the ester is saponified, and the acid thus liberated activates the chlorite. In this manner, in the course of 1-2 hours a satisfactory bleaching effect is obtained. Several factors, however, militated against any broad adoption of this method: the comparatively low speed of the bleaching action, the excessive cost of the organic esters, and the fact that the bleaching liquor containing the esters is stable, even at room temperature, only for a few hours (cf. the criticism in the article by Baier in Melliand, Textilberiohte, 1957, page 53 and following pages).

A further continuous chlorite bleaching process is covered by German Patent 945,024 and described in the article by H. W. Hund-t in the periodical SVF--Fachorgan fiir Textilveredelung der schweizerischen Vercinigung 3,120,424 Patented Feb. 4, 1964 von Fiirbereifachleuten (Trade Journal for Textile Improvement of the Swiss Association of Dyeing Experts), 10th year, (1955), pages 538-540. This method uses a neutral or alkaline solution of alkali or alkaline earth chlorites which contains no activating additions. The lack in this method of the additions provided for by the present process, results in the failure of the reference process to obtain any of the advantageous effects of the present method, in particular with respect to the intense, expeditious, uniform and non-corrosive bleaching effects. The reference process, moreover, involves the drawback of very strong corrosiveness, a fact corroborated by the recommendation of china vessels, a requirement which is quite unnecessary for purposes of the present invention. In spite of the high corrosiveness, the reference process has only a slight bleaching effect, and is mostly used in the bleaching of regenerated cellulose fiber (artificial silk, staple fiber), but not in cotton, linen, etc., i.e. native cellulose where a more forceful bleaching action is called for.

The present invention contemplates providing a continuous bleaching method free from the several drawbacks of the prior art procedures exemplified above, which comprises applying a bleaching solution to the material to be bleached, and following squeeze-01f, heating the material, the impregnation being effected with a neutral alkali chlorite solution which is either cold or heated to a temperature not exceeding 50 C., and which contains such potentially acid salts as are capable of yielding nonacidic solutions at normal room temperature, while acidifying the chlorite solutions at elevated temperatures of at least 60 C. whereby to activate the said solutions.

According to the invention, the decomposition of the alkali chlorites, and thus the activation of the bleaching solution, are controlled by the potentially acid salts incorporated in said solution. This control is effected in such a manner that by heating the squeezed-off and still moist textile material to at least 60 C., for example by the blowing-in of steam, the quantity of bleaching solution retained by the material, is activated so as to proceed to bleach the material impregnated with it.

The term potentially acid salts is intended to refer to salts which at temperatures up to 50 C. do not yield acid solutions, so as not to actitvate the chlorite bleaching liquor, but which at temperatures of at least 60 C., decompose and become strongly acid. Potentially acid salts contemplated for use according to the invention may be exemplified by salts of a strong acid and a volatile base, e.g. the ammonium salts of strong acids such as ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium phosphate, ammonium tartrate and ammonium oxalate, or the salts of strong acids with weak bases, such as magnesium chloride, calcium chloride, magnesium sulfate, calcium sulfate, magnesium phosphate, calcium phosphate, magnesium nitrate and calcium nitrate. Other potentially acid salts contemplated by the invention include the salts of strong acids with organic bases, such as triethanolamine hydrochloride, diethanolamine hydrochloride, triethylamine hydrochloride, diethylamine hydrochloride, ethylenediamine hydrochloride, etc.

Preferably, the bleaching liquors contemplated by the present invention and containing, apart from an alkali chlorite, a potentially acid salt, incorporate also a wetting agent. Any wetting agent compatible with the alkali chlorite solution is suitable for purposes of the invention. Suitable Wetting agents include alkylarylsulfonates, non-ionic wetting agents, and fatty acid condensation products.

While sodium chlorite is by far the most economic, and therefore the preferred chlorite used in the bleaching liquors of the invention, potassium and ammonium chlorite, though far less advantageous, would also be suitable. At least theoretically, the invention is not even limited to the use of alkali chlorite solutions as calcium chlorite could also be used.

The neutral alkali chlorite solution with which the textile material to be bleached is impregnated, may be either cold or mildly heated to a temperature not substantially exceeding 50 C. Once the excess bleaching liquor is squeezed off, the material thus impregnated is heated, in accordance with the invention, to a temperature of at least 60 C. While considerable activation occurs at temperatures of 60 C. and slightly above, the activation is materially stronger at temperatures of 7080 C. Heating to temperatures above 100 C. is within the province of the invention as a very strong, and very fast activation effect is observed at these higher temperatures. Above 140 C., however, a strong development of chlorine dioxide occurs which militates against further increases of the temperature.

The method of the invention is applicable to a great variety of textile materials. It is recommended for use on cellulose fibers such as cotton, staple fiber, viscose or cuprammonium rayon, linen, hemp and other bast fibers; on cellulose acetate fibers such as diacetate and triacetate fibers; on synthetic fibers such as polyamide, polyethylene-terephthalate and polyacrylonitrile fibers, to mention some representative examples. Fibers may be bleached by the present method at any stage of their manufacture, to wit: in the form of flakes, roves, fleece, yarn, felt (nonwoven material), or else when woven into fabrics, etc.

The method according to the invention may be exemplified by the following examples:

Example I A bleaching solution is prepared containing the following essential ingredients:

G. per 1.

Sodium chlorite (80 percent) 37.5 Leonil ART (Farbwerke Hochst), an aryl-alkyl sulfate 5.0

Ammonium chloride 10.0

The bleaching liquor thus prepared is used as follows: A cotton fabric is desized on a covered jigger, and then washed. Thereafter, a suction desiccator is employed to reduce the moisture content to 50 percent. The fabric is again put on the jigger and impregnated, in the cold, with a bleaching liquor of the composition noted above. The material is squeezed off lightly so the squeeze-off effect amounts to 100 percent. The excess liquor is pumped off, for use on a new section of material. At this point, the jigger is closed and heated, by a direct supply of steam, to the reaction temperature of 90-95 C. Now the material is passed through four times in order to heat the impregnated fabric to the bleaching temperature of about 90 C. Subsequently, the material is turned slowly on a jigger roller for about one hour, the jigger temperature being maintained at 95 C. by means of saturated steam. The material is twice rinsed hot, then rinsed cold, with the result that a beautiful, perfectly white fabric of excellent absorptive capacity is obtained.

Example II A cotton fabric which previously desized, rinsed and dried, is treated on an open-width bleaching frame made of stainless steel, in the following manner:

The fabric is impregnated with bleaching solution and squeezed by means of a squeezing mechanism until a squeezing effect of about 80% has been reached. The bleaching liquor contains the following essential ingredients:

G. per 1. Sodium chlorite (80 percent) 15.0 Hostapal CV (Farbwerke Hochst), a polyalkylether of a higher fatty acid 2.0

Ammonium sulfate 10.0

The solution has a pH value of about 7.5 and is used at a temperature of about 30 C.

When the squeezing is finished, the fabric is heated to about 95100 C. by means of steam or another suitable heating medium, to be maintained at this temperature for from 40 to 60 minutes. This is done most advantageously by spooling the heated fabric. This operation is followed by cold and hot rinsing, neutralization and again rinsing. The fabric is excedingly well bleached and has been rendered very highly absorbent. Cotton seed husks are largely removed and also bleached.

The above procedure may be folowed also by operating on the covered jigger referred to in Example I.

Example III A desized and dried staple fiber fabric is impregnated on the machine referred to in Example II, at about 30 C., with a bleaching liquor of the following composition:

G. per 1.

Sodium chlorite percent) 8.0 Hostapal CV (Farbwerke I-Ibchst), a polyalkylether of a higher fatty acid 1.0

Ammonium sulfate 8.0

This solution has a pH of about 7.5.

The fabric is squeezed to about of its moisture content and is heated for about 30 to 40 minutes, in the manner described in Example II, to be then finished as in Example II. The fabric is bleached beautifully and with perfect uniformity.

Example IV A blended fabric, made of a mixture of cotton and Dacron staple intimately mixed at a ratio of 65% cotton and 35% Dacron, is desized and dried. It is then impregnated at about 30 C. with a bleaching liquor containing about:

G. per 1.

Sodium chlorite (80 percent) 15.0 Sterox Se (Monsanto), a polyalkylether of a higher fatty acid 2.0

Ammonium chloride 10.0

to be then squeezed to about 60/ 70% of its moisture content. Thereafter the fabric is heated for from 40 to 60 minutes in the manner described in Example II, and then heated and finished in the manner described in Example II. A very beautifully bleached highly absorbent fabric is obtained.

The present method involves the following advantages which are at most, only partly obtained by the prior art processes exemplified above:

(1) The chlorite solution undergoes no alteration of concentration or efficacy in the course of continuous operation, with the result that even when production proceeds on a large scale, a perfect uniformity of the bleaching effect is observed.

(2) The excess liquor, left unused, is susceptible of being stored even for several days, thus resulting in a material saving of the expensive chlorite.

(3) The activation of the bleaching liquor occurs at a timely moment, and so quickly that high bleaching velocities result, at a rate unknown so far.

(4) The bleaching effect is extremely intense yet involves no damage whatever to the fiber. Cotton seed husks are bleached perfectly.

(5) The bleaching liquor itself has no corrosive properties whatever. During the heat treatment (up to C.), the development of chlorine dixoide is comparatively low so that a corrosion of stainless steel can be avoided in a simple manner.

(6) The capillarity and absorptive capacity of the bleached material are exceptionally high, properties which are highly valued in this field.

(7) The activators used in the present method are inexpensive, readily obtainable compounds.

I wish it to be understood that I do not desire to be limited to the details of composition, procedure and operation described herein as numerous modifications within the scope of the appended claims which involve neither a departure from the spirit of the invention, nor a sacrifice in the advantages thereof, may occur to workers in this field.

I claim:

1. A continuous method of bleaching textile material comprising the steps of immerging the material for a period of at least 5 seconds in a bath of a substantially neutral aqueous solution to impregnate said material with said solution, said bath having a temperature below 60 C. and containing from 0.1 to 4.0 percent of an alkali metal chlorite and from 0.1 to 2.0 percent of a salt selected from the group consisting of the chlorides, sulphates, phosphates and nitrates of magnesium and calcinm, the chloride, sulfate, phosphate, nitrate, tartrate and oxalate of ammonium, and the hydrochlorides of triethanolamine, diethanolamine, triethylamine, diethylamine, and ethylenediamine, the percentage being by weight of the textile material, removing the textile material from the bath, squeezing off my excess solution to obtain a ratio solutionztextile material between 2:1 and 1:2, and heating the moist impregnated material to a temperature between and 140 C. for a period of at least 30 minutes.

2. The method according to claim 1, wherein the material is immersed in the bath for a period of from 5 seconds to 1 hour, and the moist impregnated material is heated to a temperature between about and C., for a period of from 30 minutes to 10 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,521,340 Carr Sept. 5, 1950 2,810,717 Lamborn Oct. 22, 1957 FOREIGN PATENTS 723,566 Great Britain Feb. 9, 1955 

1. A CONTINUOUS METHOD OF BLEACHING TEXTILE MATERIAL COMPRISING THE STEPS OF IMMERGING THE MATERIAL FOR A PERIOD OF AT LEAST 5 SECONDS INA BATH OF A SUSTANTIALLY NEUTRAL AQUEOUS SOLUTION TO IMPREGNATE SAID MATERIAL WITH SAID SOLUTION, SAID BATH HAVING A TEMPERATURE BELOW 60* C. AND CONTAINING FROM 0.1 TO 4.0 PERCENT OF AN ALKALI METAL CHLORITE AND FROM 0.1 TO 2.0 PERCENT OF A SALT SELECTED FROM THE GROUP CONSISTING OF THE CHLORIDES, SULPHATES, PHOSPHATES AND NITRATES OF MAGNESIUM AND CALCIUM, THE CHLORIDE, SULFATE, PHOSPHATE, NITRATE, TARTRATE AND OXALATE OF AMMONIUM, AND THE HYDROCHLORIDES OF TRIETHANOLAMINE, DIETHANOLAMINE, TRIETHYLAMINE, DIETHYLAMINE, AND ETHYLENEDIAMINE, THE PERCENTAGE BEING BY WEIGHT OF THE TEXTILE MATERIAL, REMOVING THE TEXTILE MATERIAL FROM THE BATH, SQUEEZING OFF MY EXCESS SOLUTION TO OBTAIN A RATIO SOLUTION:TEXTILE MATERIAL BETWEEN 2:1 AND 1:2, AND HEATING THE MOIST IMPREGNATED MATERIAL TO A TEMPERATURE BETWEEN 60* AND 140*C. FOR A PERIOD OF AT LEAST 30 MINUTES. 